Trauma, lumbar burst fractures, tumors, severe disc degeneration, and anterior fusion following multiple posterior operations, are just some of the causes of anterior thoraco-lumbar spinal instability. Anterior treatment of thoraco-lumbar spinal instability has included the use of a conventional fixation system comprised of a generally planar plate and fasteners. The plate is arranged between a pair of vertebrae, and has openings for receiving the fasteners. The fasteners engage the appropriate vertebra to affix the plate thereto.
Prior art fixation systems have several disadvantages. In this respect, the fixation systems have relatively flat plates that connect to the vertebrae by some combination of bolts or screws. Loading of such an implant system is primarily onto the smallest, weakest, and least stiff components of the fixation system. The entire load is taken by the screws at one end of the plate, and transferred through the plate to the screws at the other end of the plate. Furthermore, maximal stress on the plate occurs at the tensile (lateral) side of the plate. Accordingly, the stiffness, strength and fatigue properties of prior art fixation systems are deficient.
Moreover, prior art fixation systems have a profile that matches only the anterior profile of the vertebral bodies. As a result, surgeons are forced to cut a channel in the bone in order for the plate to fit properly. This leads to complex surgical procedures, long implantation times, and an anatomical fit which does not allow for biomechanical load-sharing which leads to improvements in mechanical properties such as stiffness, strength and fatigue life.
The present invention addresses these and other drawbacks of prior art bone fixation systems.